coverage: Remove all unstable support for MC/DC instrumentation

compiler/rustc_session/src/config.rs

@@ -190,7 +190,7 @@ pub struct CoverageOptions {
     pub discard_all_spans_in_codegen: bool,
 }
 
-/// Controls whether branch coverage or MC/DC coverage is enabled.
+/// Controls whether branch coverage is enabled.
 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, Default)]
 pub enum CoverageLevel {
     /// Instrument for coverage at the MIR block level.
@@ -214,9 +214,6 @@ pub enum CoverageLevel {
     /// instrumentation, so it might be removed in the future when MC/DC is
     /// sufficiently complete, or if it is making MC/DC changes difficult.
     Condition,
-    /// Instrument for MC/DC. Mostly a superset of condition coverage, but might
-    /// differ in some corner cases.
-    Mcdc,
 }
 
 // The different settings that the `-Z offload` flag can have.

compiler/rustc_session/src/options.rs

@@ -755,7 +755,7 @@ mod desc {
     pub(crate) const parse_linker_flavor: &str = ::rustc_target::spec::LinkerFlavorCli::one_of();
     pub(crate) const parse_dump_mono_stats: &str = "`markdown` (default) or `json`";
     pub(crate) const parse_instrument_coverage: &str = parse_bool;
-    pub(crate) const parse_coverage_options: &str = "`block` | `branch` | `condition` | `mcdc`";
+    pub(crate) const parse_coverage_options: &str = "`block` | `branch` | `condition`";
     pub(crate) const parse_instrument_xray: &str = "either a boolean (`yes`, `no`, `on`, `off`, etc), or a comma separated list of settings: `always` or `never` (mutually exclusive), `ignore-loops`, `instruction-threshold=N`, `skip-entry`, `skip-exit`";
     pub(crate) const parse_unpretty: &str = "`string` or `string=string`";
     pub(crate) const parse_treat_err_as_bug: &str = "either no value or a non-negative number";
@@ -1458,7 +1458,6 @@ pub mod parse {
                 "block" => slot.level = CoverageLevel::Block,
                 "branch" => slot.level = CoverageLevel::Branch,
                 "condition" => slot.level = CoverageLevel::Condition,
-                "mcdc" => slot.level = CoverageLevel::Mcdc,
                 "discard-all-spans-in-codegen" => slot.discard_all_spans_in_codegen = true,
                 _ => return false,
             }

compiler/rustc_session/src/session.rs

@@ -354,11 +354,6 @@ impl Session {
             && self.opts.unstable_opts.coverage_options.level >= CoverageLevel::Condition
     }
 
-    pub fn instrument_coverage_mcdc(&self) -> bool {
-        self.instrument_coverage()
-            && self.opts.unstable_opts.coverage_options.level >= CoverageLevel::Mcdc
-    }
-
     /// Provides direct access to the `CoverageOptions` struct, so that
     /// individual flags for debugging/testing coverage instrumetation don't
     /// need separate accessors.